Split head clamping fasteners have long been known, especially in the electrical connector art. Examples of such fasteners are found in U.S. Pat. Nos. 368,149; 1,809,381; 2,406,346; and 2,440,828 for holding an electrical wire which passes through that portion of the fastener which is a collet having a radially split head. The head has an increasing outer diameter, resembling a cone, which is to mate with a ferrule having a funnel shaped interior. The body of the collet is threaded and, after passing through the ferrule, is secured by a collet nut, which draws the conic head further into the ferrule and thereupon forces the segments of the split head radially inward against the work piece, an electrical cable. The ferrule itself is fastened to a main body, such as an electrical panel or battery.
Although this prior art type of fastener is useful, it is limited by the fact that it requires several mating parts as well as mechanical access to both ends of the ferrule; one end for inserting the collet and the other end for threading the collet nut. The fact that the fastener itself must be secured to a primary support further limits its versatility. Also, the mechanical force necessary to draw the collet into the ferrule requires a threaded pair of parts and a hand tool for tightening the collet nut.
Swedish patent No. 87,205 discloses a clamping device in which tightening a nut on a threaded, slotted shaft reduces the interior shaft diameter, causing a clamping action of a tubular workpiece held in the shaft. U.S. Pat. No. 1,615,233 shows a similar type of clamp, in which tightening a nut on a conical, segmented head draws the segments together to produce a clamping action. U.S. Pat. No. 2,383,692 and French patent No. 2,442,392 show similar types of split shaft clamps in which tightening a nut on a conical, segmented shaft produces clamping action on a workpiece held in the shaft.
More recently, U.S. Pat. Nos. 4,530,523 and 4,544,186 teach a clamping device in which clamping is produced by a pivoting action of threaded shaft segments. Here a nut carried on the shaft forcibly abuts a clamp surface, as the nut is tightened, and the reaction force is transmitted through the action of the bevelled nut threads to the bevelled shaft threads, to cause a slight pivoting in the clamp segments, to produce clamping of a workpiece held in the shaft.
It will be appreciated that all of the later-mentioned prior art clamp devices have a slotted shaft designed to produce a clamping action as a nut is advanced along the threaded shaft. One limitation of this construction is that clamping action requires interaction with a threaded nut, and thus precludes for example, the possibility of a simple screw-like shaft which can be engaged with a wall surface or the like, for clamping a workpiece to a wall surface. Secondly, each clamp member must be fully duplicated in a two-sided clamp, i.e., a clamp designed to clamp two workpieces together. Such devices are also limited to threaded engagement between a shaft and nut, and thus require turning in order to achieve clamping action.